This invention relates in general to magnetostatic wave (MSW) devices and relates more particularly to MSW resonators. In FIG. 1 is presented a previous MSW resonator. In MSW wave devices, a magnetic medium is utilized to transport magnetostatic waves. An input transducer responsive to applied electromagnetic signals launches the waves in the magnetic medium and an output transducer responsive to the MSW waves generates output signals.
In FIG. 1 is illustrated a previous MSW resonator. In this resonator, a thin film 11 of a ferrimagnetic material such as yttrium iron garnet (YIG) is grown by liquid phase epitaxy (LPE) on a gadolinium gallium garnet (GGG) substrate. The YIG film is utilized as the magnetic medium in which magnetostatic waves are transported. A first microstrip conductor 12 is formed adjacent to YIG film 11 and parallel to a side 14 of the film. This microstrip conductor functions as an input transducer. When an electrical signal is applied to microstrip conductor 12, the resulting current in this conductor produces a magnetic field encircling this conductor. This field pushes on the magnetic dipoles in the YIG film, thereby launching MSW waves in the YIG film in a direction k perpendicular to axis 14 of microstrip conductor 12. The vector k is the wavevector of the MSW waves induced in film 11. The magnitude k of k (also referred to as the wavenumber) is equal to 2.pi. divided by the wavelength of the magnetostatic wave. For the orientation shown in FIG. 1, k is in the negative y direction. A second microstrip conductor 15 is responsive to the MSW waves YIG film 11 and functions as the output transducer of the resonator.
YIG film 11 is in the form of a rectangle of width L.sub.x and length L.sub.y. In such a rectangular YIG film, the fundamental MSW modes are of the forms in(k.sub.x .multidot.L.sub.x).multidot.sin(k.sub.y .multidot.L.sub.y). Resonances occur when k.sub.x .multidot.L.sub.x /.pi. is equal to some integer m and k.sub.y .multidot.L.sub.y /.pi. is equal to some integer n. The relationship between the frequency f.sub.mn of this resonance and the magnitude k.sub.mn of this resonance is nonlinear and depends on the direction of application of a bias field H.sub.0 that is applied to the YIG film. When H.sub.0 is parallel to the surface of the YIG film and is parallel to the microstrip conductors, the resulting magnetostaic waves are referred to as surface waves. When H.sub.0 is parallel to the surface of the YIG film and perpendicular to the microstrip conductors, the resulting magnetostatic waves are referred to as backward volume waves. When H.sub.0 is perpendicular to the surface of the YIG film, the resulting magnetostatic waves are referred to as forward volume waves. In general, there is a non-linear relationship between the angular frequency .omega.=2.pi.f and the wavenumber k. This relationship is shown in FIG. 2 for all three orientations of H.sub.0. In this figure, the anisotropic field is the magnetic field introduced by the anistropic structure of the crystal structure of the YIG film. For surface waves and forward volume waves, the frequency is an increasing function of wavenumber, but for backward volume waves it is a decreasing function of frequency. For surface waves and forward volume waves, the lowest order resonance occurs when m and n are both equal to 1.
In order to suppress excitation of the resonances for m.noteq.1, microstrip conductors 12 and 15 were aligned parallel to side 13 to a high degree of accuracy. In addition, other techniques can be utilized to suppress these unwanted (spurious) resonances for m.noteq.1 (see, for example, copending U.S. patent application Ser. No. 17/094,963 entitled MODE SELECTIVE MAGNETOSTATIC WAVE RESONATORS filed by Kok Wai Chang, et al on 9/2/87). Such precise alignment and the inclusion of these other modes of suppression of these spurious modes increases the cost of these resonators. Therefore, it would be advantageous to have a new, simpler and less expensive means of suppressing the unwanted resonances and of channelling a greater fraction of the input signal into the resonant mode of interest.